Projectors are devices adapted for projecting image information from different sources on a surface. The image information can be still images (photographies, slides, computer displays, etc.) or moving (videos, animations, etc.) and can be provided by different sources like, for instances, a computer connected to the projection device, multimedia player (DVD, Blueray players), TV tuner, etc.
The projector subsystem can also be embedded inside a communication terminal like a smartphone, a tablet, a laptop computer, etc. and then be able to use the content of the communication system as sources and project any files stored inside the communication system. This type of projector is usually referred to as “pico-projector”, and is constrained in size and power consumption so as to be embedded in a more complex system, often a handheld device.
Projectors, including pico-projectors, are often based on laser technology for projecting images. Usually, one laser per color component (red, green, blue) is used.
However, lasers (as well as light beams above a certain power) may be armful or dangerous when directed towards the eyes.
Even when warned about this potential danger, many situations can imply risks. For instance, a speaker may be so concentrated by his speech that he can enter the projection area and face the projector without noticing immediately.
The potentially risk situations even increase with handheld devices embedding pico-projectors: for instance, the user may be willing to look around for the best projection surface and then point the projection beam towards other people. Also, the handheld device can be used by children less aware of safety issues. Even malicious behaviors should be taken into account.
It appears then clearly that there is a need for safety features for projectors, especially for pico-projectors embedded in handheld devices.
Some safety solutions have been proposed to avoid projection beams being directed towards the eyes.
For instance, the patent application US2010/0177929 proposes a solution where the projector device also comprises a camera to capture the projected image. The device then analyses the image and uses face-recognition algorithms to determine if a human face (or other body features) is present and in this case switch off the projection beam.
A major drawback of this solution is the confusion that can be made between a real human face and a projected human face. The camera is unable to make this distinction and this mechanism detects the presence of a human in front of the projector each time the projected image contains a human face (or any other human body feature used to detect a human presence).
Other solutions, like the one described in the U.S. Pat. No. 6,002,505, are based on sensors measuring acoustic signals, electromagnetic radiations, infrared signals etc. They have as major drawbacks to not be robust enough and to make use of additional and costly devices to be embedded within the projection subsystem. In addition, these sensors can be subject to interferences with other devices in the vicinity.